Scenarios when you need to configure your modem in bridge mode
When two NAT devices are connected in series (for instance a Modem with built-in NAT capabilities is connected to a Router which is also a NAT device), its advisable you configure your modem in bridge mode to avoid conflicts.
What is NAT?
In computer networking, the process of Network Address Translation (NAT) involves re-writing the source and/or destination address of IP packets as they pass through a router. NAT allows multiple hosts on a private network to access the Internet using a single public IP address.
What is Bridge Mode?
Bridge mode is the configuration that disables the NAT feature on the modem and allows a router to function as a DHCP server without an IP Address conflict.
Modem has to be bridged before connecting to a router since the applications like VPN, P2P, remote management, etc. requires a public IP Address on the routers WAN port for a successful connection. You will need to call your Internet Service Provider for Bridge mode settings.
Here is a list of common service providers and modems that may require setting modem to bridge mode (please note that this list identifies only the common models and does not cover all modems):